Press plates or endless belts are being used for producing material sheets, for example wood material sheets, which are provided with a respective decorative design. Alternative applications can be found in the production of laminate panels or laminate floor plates. The material sheets employed include a core made from MDF or HDF, wherein different material layers are applied at least on one side, wherein the material layers can included for example a decorative layer and a protective overlay layer. In order to prevent warping of the material sheets used, typically the backside is also provided with respective material layers, so that the material sheet can be pressed together in a press using press plates or endless belts. Advantageously, hot presses are used for this purpose, since the different applied material layers are impregnated with duro-plastic resins, for example melamine resin, and thus melt together with the surface of the core under heat impact. Thus, the employed decorative layers can be structured, wherein for example a wood or tile décor can be embossed, or structures are being used that have an artistic design corresponding to the respective application. In order to improve a natural reproduction, in particular for wood decors, tile decors or natural stone surfaces, and for obtaining particular gloss grades, press plates and endless belts are being used, which include a negative image of the provided structure. The quality of the material sheets produced with a decorative layer and an embossed pattern thus achieves high precision based on digitized printing techniques and digitized production of the press plate surfaces, wherein the precision comes very close to natural wood panels or comparable materials due to the precise alignment. Adjusting a particular gloss grade furthermore provides the option to generate reflections or shadings which convey an impression of a natural wood surface or an impression of other materials to a user.
In order to achieve the result recited supra, the quality requirements for the production of the press plates, endless belts and cylindrical embossing rollers are high, which facilitates in particular precision fabrication with the provided decorative layers. The press plates and endless belts are thus being used as top tools and bottom tools in quick cycle presses, which are provided with press plates or double band presses, which are provided with endless belts, wherein the embossing and heating of the material layers is performed simultaneously, so that the duro-plastic resins are connected with the core through melting and hardening. The embossing rollers, on the other hand, are rolled over the surface of a material sheet and are also being used for structuring.
Methods are known in the art for producing the press plates, endless belts or embossing rollers, wherein the methods provide an application of an etching resistant layer with a respective structure onto a pretreated metallic surface, a subsequent etching process in order to generate a first structure on the surface through an etching process, and subsequent removal of the etching resistant layer. Depending on the desired surface quality, this etching process can be repeated several times in sequence, so that a particularly high penetration depth into the surface of the press plate or of the endless belts can be achieved, and additionally a coarse and fine structuring can be achieved that provides the desired structure layout. Thus, a mask is applied through a silk screening method to a pretreated plate after cleaning has been performed, and the desired surface structure is generated through subsequent etching, wherein the silk screening is applied to the large format plates and the plates are subsequently etched on their entire surfaces. All portions which form the high surface structures are thus covered through the applied mask, so that surface etching can only be performed in the portions which are directly exposed to the etching liquid. The etched out portions then form the profile depressions of the desired structure. After the etching has been performed, the surface is cleaned and in particular the mask removed, so that the surface treatment can continue and the surface can be subjected to another finishing process, for example hard chroming.
Alternatively, there is the option to use a photographic method, in which initially a photosensitive layer is applied to the entire surface. The photosensitive layer subsequently has to be exposed according to the provided mask in order to create the surface structure. Thereafter, the photosensitive layer needs to be developed. In between, numerous flushing processes have to be performed, so that the surface can be prepared and cleaned for the subsequent process steps. After the development of the photosensitive layer, this creates a mask which is also designated as etching template or etching resistant layer. The reproducibility of the masks produced in this manner is problematic, because the negative or positive image always has to be positioned in an exactly identical position relative to the photosensitive layer in order to expose the light sensitive layer, when more than one exposing and etching process shall be performed after the other, in order to thus apply complex 3D structures to the surface of a press plate or endless belt. This is problematic in particular when the negative or positive image is directly applied to the light sensitive layer in order to expose the light sensitive layer, and the negative or positive image does not have exactly the same distance at each position of the photosensitive layer. The reproducibility of applying the mask required for obtaining high imaging precision is thus not always assured, in particular for a photographic method. Additional problems can be created when a 3D structure shall be achieved through plural exposing and etching processes required in sequence, and thus plural masks have to be applied for this purpose after one another in sequence, wherein an etching process is performed between each mask application. Through the precise positioning and the required number of respective masks, thus the production of the press plates or of the endless belts is very complex and expensive. The resolution of the surface structure thus is highly dependent on the mask to be applied and dependent on the method employed, and furthermore uses a substantial number of process steps, wherein complex handling is used in particular due to the size of the press plates or of the endless belts.
Lately, the masks have been applied to the press plate directly, for example with an inkjet printer instead of a photographic method or a silk screening method, wherein digitized data is being used. This measure assures that an exact and precise image can be applied several times onto the same surface portions, so that a particularly deep structuring, this means etching of the surface can be performed. However, also for this method, numerous etching processes are used, which are detrimental to the environment.